<template>
   <div class="list">
     <div
       class="item"
       v-for="item of letters"
       :key="item"
       :ref="item"
       @touchstart="handleTouchStart"
       @touchmove="handleTouchMove"
       @touchend="handleTouchEnd"
       @click="handleLetterClick">{{item}}</div>
   </div>
</template>

<script>
export default {
  name: 'CityAlphabet',
  props: {
    cities: Object
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  data () {
    return {
      touchStatus: false
    }
  },
  methods: {
    handleLetterClick (e) {
      this.$emit('change', e.target.innerText)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (this.touchStatus) {
        const startY = this.$refs['A'][0].offsetTop
        const touchY = e.touches[0].clientY - 79
        const index = Math.floor((touchY - startY) / 20)
        if (index >= 0 && index < this.letters.length) {
          this.$emit('change', this.letters[index])
        }
      }
    },
    handleTouchEnd () {
      this.touchStatus = false
    }
  }
}
</script>

<style lang="stylus" scoped>
 @import '~$styles/variables.styl'
 .list
   display: flex
   flex-direction: column
   justify-content: center
   position: absolute
   top: 1.58rem
   right: 0
   bottom: 0
   width: .4rem
   .item
     line-height: .4rem
     text-align: center
     color: $bgColor
</style>
